1. Field of the Invention
The present invention relates to a method of reducing shield shorts in a high linear density read head with a contiguous junction and, more particularly, to such a method wherein a first read gap layer is refilled after being overmilled and side walls of a sensor are cleaned before making a contiguous junction.
2. Description of the Related Art
The heart of a computer is a magnetic disk drive which includes a rotating magnetic disk, a slider that has read and write heads, a suspension arm above the rotating disk and an actuator arm that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. When the disk is not rotating the actuator arm parks the suspension arm and slider on a ramp. When the disk rotates and the slider is positioned by the actuator arm above the disk, air is swirled by the rotating disk adjacent an air bearing surface (ABS) of the slider causing the slider to ride on an air bearing a slight distance from the surface of the rotating disk. The ABS is an exposed surface of the slider and the write and read heads that face the rotating disk. When the slider rides on the air bearing, the actuator arm positions the write and read heads over the selected circular tracks on the rotating disk where signal fields are written and read by the write and read heads. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
An exemplary high performance read head employs a giant magnetoresistance (GMR) read sensor for sensing magnetic signal fields from the rotating magnetic disk. The GMR read sensor comprises a nonmagnetic electrically conductive spacer layer that is sandwiched between a ferromagnetic pinned layer and a ferromagnetic free or sense layer. An antiferromagnetic pinning layer typically interfaces the pinned layer for pinning the magnetization of the pinned layer 90° to an air bearing surface (ABS) of the read sensor wherein the ABS of the read sensor is an exposed surface of the read sensor that faces the rotating disk. First and second hard bias and lead layers are typically connected to the read sensor for conducting a sense current therethrough. The magnetization of the free layer is free to rotate upwardly and downwardly with respect to the ABS from a quiescent or zero bias point position in response to positive and negative signal fields respectively from the rotating magnetic disk. The quiescent position of the magnetization of the free layer, which is parallel to the ABS, is when the sense current is conducted through the read sensor without signal fields from the rotating magnetic disk.
When a sense current is conducted through the read sensor, electrical resistance changes of the sensor cause potential changes that are detected and processed as playback signals by processing circuitry. The sensitivity of the read sensor is quantified by a giant magnetoresistance (GMR) coefficient ΔR/R where ΔR is the change in resistance of the read sensor from minimum resistance (when magnetizations of free and pinned layers are parallel to each other) to maximum resistance (when magnetizations of the free and pinned layers are antiparallel to each other) and R is the resistance of the read sensor at minimum resistance.
First and second hard bias and lead layers are typically connected to first and second side surfaces of the read sensor, which connection is known in the art as a contiguous junction. This junction is described in commonly assigned U.S. Pat. No. 5,018,037 which is incorporated by reference herein. The first and second hard bias layers longitudinally stabilize the magnetization of the free layer of the GMR sensor in a single domain state which is important for proper operation of the GMR sensor.
A read head is rated by its areal density which is a product of its track width density and its linear bit density. The track width density is quantified as the number of tracks per inch (TPI) along a radius of the disk while the linear bit density is quantified as the number of bits per linear inch (BPI) along the track of the disk. The track width density is dependent upon the width of the sensor at the ABS while the linear density is dependent upon the spacing between the first and second shield layers. In a typical read head the sensor is located between nonmagnetic electrically insulative first and second read gap layers which are, in turn, located between the first and second shield layers. Consequently, it is important to minimize thicknesses of the first and second read gap layers so as to reduce the read gap between the first and second shield layers. A typical material for the first and second read gap layers is aluminum oxide (Al2O3). Unfortunately, when the read gap layers are made too thin pinholes in these layers cause electrical shorts between the shield layers and the first and second lead layers. For instance, if the first read gap layer has a pinhole this will cause a short between the first shield layer and one of the first and second lead layers to the sensor. This can be overcome by making the first read gap layer sufficiently thick so that a pinhole does not extend through the thickness of the layer. Making the aforementioned contiguous junction can present a problem in maintaining the first read gap layer with an optimized reduced thickness that is free of pinholes.
In the making of the read head the first read gap layer is sputter deposited on the first shield layer, a sensor material layer is formed on the first read gap layer, a mask with a desired track width is formed on the sensor material layer and exposed portions of the sensor material layer are milled to form a sensor with first and second side walls that are spaced apart by the track width. In order to ensure that all portions of the sensor material layer extending laterally from the first and second side walls of the sensor are removed, it is necessary to overmill into the first read gap layer. This causes the first read gap layer to have first and second depressions which extend laterally from the first and second side walls of the sensor. The first and second hard bias and lead layers are then formed in these depressions and electrically connected to the first and second side walls of the sensor. Unfortunately, the reduced thickness of the first read gap layer presents a high risk that there will be a shield short between the first shield layer and one of the first and second hard bias and lead layers. If the first read gap layer is formed with a sufficient thickness so that the overmilling does not cause a risk of pinholes, this increased thickness reduces the linear bit read density of the read head. There is a strong-felt need to maintain an optimized narrow first read gap layer without the risk of pinholes while ensuring the removal of the sensor material layer extending laterally from the first and second side walls of the sensor and making a contiguous junction that has high electrical contact between the side walls of the sensor and the first and second hard bias and lead layers.